1996 Chevy Truck fuel pressure

Engine problem
1996 Chevy Truck V8 Four Wheel Drive Automatic 169.00 miles

I changed a fuel pump on my 1 ton dually maybe 1 year ago.
and sence it has has been slower starting and very slugish when not completly wormed up. The check engine light has also beeb on sence. I took it to auto prts store and there computer say low fuel pressure.
Today I changed the fuel pump again thinking the other parts store sold me the wrong one. Well it made no difference. Did I or is it possible to put the fule pump liin and the return line on backwords ayear ago and did the same today. Iknow they are the same fittings butwill it even run if they where backword?